First time letting broody hatch

Hi- My Silkie is at day 19. I candled a few days ago and two of the eggs had nothing developing. Just wondering if I should take them from her or just leave them until others hatch? She's only sitting on 4 so I wasn't sure if she might bail if some eggs were missing. Also I have her in a separate area in the coop. About how long before mom decides to venture out with them? Temps have been up and down in NJ so I just want to keep a close eye.

If they aren't developing it's safe to leave them. Eggs explode when bacteria gets into an egg via being cracked or having a dead embryo in it. She will sit for a 2-3 days (just in case any more eggs miraculously hatch) then venture out to feed and water them. Remember to only let them have access to shallow water or they could fall in and drown. And keep an eye on your other birds. If she isn't assertive enough they could kill the chicks. Good luck.